Hey all ... looking for some advice.

I have put together plans for a decent-sized playscape for our four kids in the backyard. It's got two decks (one at ground level and another 5-feet above that), with a small playhouse built on the top deck, and a swingset mounted off the side of the top deck as well.

In all honesty, I consider myself a fairly handy guy, but this will be the first time undertaking anything like this.

But in planning everything out, I have a couple of questions that I want some more input on before we move ahead.

1) How should I anchor it? I'm looking at using 6x6 posts. Should I use these steel brackets in concrete to anchor them? Or should I just sink the posts straight into the concrete itself like I've seen done with fence posts?

2) I'm a bit torn regarding lumber materials. My wife and I are a bit hesitant toward PT lumber. It doesn't have a nice history, and as a scientist, she is quick to note that the way those histories play out is that people realize years later that what they thought was perfectly safe ... wasn't. And this is our kids, who are most likely going to find a way to touch every stinking inch of this structure in one way or another.

I'm OK using it for joists and such under the lower deck that will be close to the ground. But since we're going to stain or paint the whole thing anyways, we'd like to use untreated wood for the rest. The general "construction lumber" that they have the big box hardware stores around us would probably be fine for most of what we're doing. However, they do not seem to have deck surface planks (with the nice rounded corners and all that) available in anything but PT lumber and cedar. That leads me to believe that using something like untreated pine (even maybe southern yellow pine) would be hard for us to find.

We don't have a lot of money to spend on it, and most discussions about decking keep suggesting that we should all be using rare, expensive hardwoods from the rainforest or some such (which we're not too keen on either). It's ultimately a temporary structure ... our kids will all outgrow it within 7-10 years anyways.

So I'm just looking for some advice about easy-to-find, relatively inexpensive lumber that will take a stain and last for about 7 years or so.

ANY advice would be greatly appreciated. Thank you!